Drug binding to recognition sites for endogenous ligands can act as agonists and antagonists. An imidazobenzodiazepine derivative, RO 15-1788 is the first representative of specific benzodiazepine antagonists. However, since anxiolytic benzodiazepines probably act as antagonists, the RO 15-1788 may be acting as an agonist, that is it mimics the endogenous agonist. Studies with isoniazid show that benzodiazepines antagonize the convulsant action of isoniazid, while RO 15-1788 facilitates these convulsions. It has been reported that Beta-carbolines bind to benzodiazepine recognition sites in brain. These drugs, however, differ from benzodiazepines because they are convulsant or proconvulsant. Behavioral studies with Beta-carbolines indicate that these drugs unveil latent conflict behavior in rat. The possibility that Beta-carbolines and RO 15-1788 mimic the action of an endogenous anxiogenic agent is at present under investigation.